Method and system for coupling SOEC-molten carbonate fuel cell to electrolyze carbon dioxide and water

Abstract

The invention relates to the field of SOEC hydrogen production and molten carbonate fuel cell power generation, and discloses a method and a system for coupling SOEC-molten carbonate fuel cell electrolysis of carbon dioxide and water, and the method comprises the following steps: (1) feeding hydrogen-rich gas into an anode of a molten carbonate fuel cell, feeding CO2-poor gas and oxygen-containing gas into a cathode of the molten carbonate fuel cell, and feeding oxygen into the cathode of the molten carbonate fuel cell; direct electrochemical power generation is carried out; (2) performing catalytic combustion on anode tail gas of the molten carbonate fuel cell to obtain CO2-rich mixed gas; (3) feeding the CO2-rich mixed gas into a hydrogen electrode side of a solid oxide electrolytic tank, feeding oxygen-containing gas into an oxygen electrode side of the solid oxide electrolytic tank, and carrying out a co-electrolysis reaction; and (4) returning the produced gas on the hydrogen electrode side of the solid oxide electrolytic tank to the step (1) to provide at least part of hydrogen-rich gas. According to the method, a solid oxide electrolysis stack and a molten carbonate fuel cell are systematically coupled, so that the trapping and recycling of carbon dioxide are realized.

Description

Technical Field

[0001] This invention relates to the field of solid oxide electrolysis technology, and more specifically to a method and system for electrolyzing carbon dioxide and water using a coupled SOEC-molten carbonate fuel cell. Background Technology

[0002] Solid oxide electrolysis (SOEC) is a highly efficient energy conversion device that converts electrical and thermal energy into the chemical energy of fuels such as hydrogen, methanol, and natural gas. Compared with other electrolysis technologies, SOEC has the outstanding advantages of low energy consumption and high efficiency. It can be used for high-temperature co-electrolysis of CO2 / H2O and can efficiently produce syngas (CO+H2). With its advantages of high efficiency, low emissions, low pollution, and wide range of applications, SOEC has become one of the most popular energy conversion technologies and has great research potential, attracting widespread international attention.

[0003] Molten Carbonate Fuel Cell (MCFC) is a high-temperature fuel cell operating at 650°C. This technology can enrich low-concentration CO2 introduced from the cathode to the anode during power generation, achieving low-cost CO2 capture while generating electricity. If this technology is coupled with SOEC, it is expected to achieve near-zero emissions of pollutants, including carbon dioxide, at low cost, opening up a new path for the clean and efficient use of fossil energy and potentially triggering a technological revolution in coal-based energy. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of low utilization rate and high capture cost of low-concentration carbon dioxide in the existing fossil energy power generation process, and to provide a method and system for electrolyzing carbon dioxide and water by coupling SOEC-molten carbonate fuel cell. This method can enrich the low-concentration carbon dioxide emitted from fossil energy power generation through molten carbonate fuel cell power generation technology, and further convert it into fuel cell gas through solid oxide electrolysis cell, thereby achieving near-zero emissions of pollutants from fossil energy power generation.

[0005] To achieve the above objectives, the present invention provides a method for electrolyzing carbon dioxide and water using a coupled SOEC-molten carbonate fuel cell, the method comprising:

[0006] (1) Hydrogen-rich gas is fed into the anode of the molten carbonate fuel cell, and CO2-deficient gas and oxygen-containing gas are fed into the cathode of the molten carbonate fuel cell for direct electrochemical power generation.

[0007] Wherein, the volume content of CO2 in the lean CO2 gas is not higher than 20%;

[0008] (2) Catalytically combust the anode tail gas of the molten carbonate fuel cell to obtain a CO2-rich mixture;

[0009] (3) The CO2-rich mixed gas is fed into the hydrogen electrode side of the solid oxide electrolytic cell, and the oxygen-containing gas is fed into the oxygen electrode side of the solid oxide electrolytic cell for co-electrolysis reaction.

[0010] (4) Return the generated gas from the hydrogen electrode side of the solid oxide electrolyzer to step (1) to provide at least a portion of the hydrogen-rich gas.

[0011] A second aspect of the present invention provides a system for electrolyzing carbon dioxide and water using a coupled SOEC-molten carbonate fuel cell, the system comprising an anode gas supply unit, a cathode gas supply unit, a molten carbonate fuel cell unit, a catalytic burner, and a solid oxide electrolysis unit.

[0012] The anode gas supply unit includes a fuel gas supply device and a fuel processor connected in sequence;

[0013] The cathode gas supply unit includes a flue gas supply device, an air supply device, and a mixer that is connected to the flue gas supply device and the oxygen-containing gas supply device respectively.

[0014] The molten carbonate fuel cell unit includes a molten carbonate fuel cell, and the solid oxide electrolysis unit includes a solid oxide electrolyzer.

[0015] The anode gas supply unit is connected to the anode inlet of the molten carbonate fuel cell and is used to provide hydrogen-rich gas; the cathode gas supply unit is connected to the cathode inlet of the molten carbonate fuel cell and is used to provide CO2-lean gas and oxygen-containing gas.

[0016] The anode exhaust outlet of the molten carbonate fuel cell is connected to the feed inlet of the catalytic burner, which is used to send the anode exhaust gas of the molten carbonate fuel cell into the catalytic burner for catalytic combustion to obtain a CO2-rich mixture.

[0017] The outlet of the catalytic burner is connected to the hydrogen electrode side inlet of the solid oxide electrolysis cell, and the oxygen electrode side inlet of the solid oxide electrolysis cell is connected to the oxygen-containing gas supply device, so that the CO2-rich mixed gas and the oxygen-containing gas are sent into the hydrogen electrode side of the solid oxide electrolysis cell for co-electrolysis reaction.

[0018] The gas outlet on the hydrogen electrode side of the solid oxide electrolyzer is connected to the anode gas supply unit to provide at least a portion of the hydrogen-rich gas to the gas produced on the hydrogen electrode side of the solid oxide electrolyzer.

[0019] This invention utilizes the electrochemical reaction of a molten carbonate fuel cell to achieve low-cost carbon dioxide enrichment during power generation; it uses an SOEC stack to co-electrolyze CO2 and H2O to produce a mixed gas of CO and H2, providing a fuel gas source for the molten carbonate fuel cell; and it couples the solid oxide electrolyzer with the molten carbonate fuel cell to achieve carbon dioxide capture and reuse. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of a system for electrolyzing carbon dioxide and water using a coupled SOEC-molten carbonate fuel cell, according to one embodiment of the present invention. Detailed Implementation

[0021] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0022] The first aspect of this invention provides a method for electrolyzing carbon dioxide and water using a coupled SOEC-molten carbonate fuel cell, the method comprising:

[0023] (1) Hydrogen-rich gas is fed into the anode of the molten carbonate fuel cell, and CO2-deficient gas and oxygen-containing gas are fed into the cathode of the molten carbonate fuel cell for direct electrochemical power generation.

[0024] Wherein, the volume content of CO2 in the lean CO2 gas is not higher than 20%;

[0025] (2) Catalytically combust the anode tail gas of the molten carbonate fuel cell to obtain a CO2-rich mixture;

[0026] (3) The CO2-rich mixed gas is fed into the hydrogen electrode side of the solid oxide electrolytic cell, and the oxygen-containing gas is fed into the oxygen electrode side of the solid oxide electrolytic cell for co-electrolysis reaction.

[0027] (4) Return the generated gas from the hydrogen electrode side of the solid oxide electrolyzer to step (1) to provide at least a portion of the hydrogen-rich gas.

[0028] The method for electrolyzing carbon dioxide and water using a coupled SOEC-molten carbonate fuel cell provided by this invention generates electricity through an electrochemical reaction within the molten carbonate fuel cell. Simultaneously, low-concentration carbon dioxide from the cathode side is enriched on the anode exhaust gas side. After catalytic combustion of the anode exhaust gas, water vapor is separated to obtain high-concentration carbon dioxide, achieving low-energy and low-cost carbon dioxide capture during power generation. By combining molten carbonate fuel cell power generation technology with fossil fuel power generation and hydrogen production technology, the enriched carbon dioxide combined with water vapor is further co-electrolyzed in a solid oxide electrolyzer to produce a mixture of CO and H2. This mixture can be directly introduced into the molten carbonate anode, achieving near-zero carbon dioxide emissions at low cost.

[0029] In this invention, the molten carbonate fuel cell has the conventional definition in the art. The molten carbonate fuel cell generally includes an anode, an electrolyte layer, a cathode, and bipolar plates that assemble single cells into a fuel cell stack. Its electrolyte is molten carbonate. This invention does not impose any particular limitation on the specific materials of the components in the molten salt fuel cell; any conventional choice in the art can be used.

[0030] According to the present invention, preferably, the operating temperature of the molten carbonate fuel cell is 620-650°C.

[0031] In this invention, the power and number of cells in the molten carbonate fuel cell can be calculated based on the gas source. According to some preferred embodiments of the invention, relative to 100 Nm... 3 With a CO2 concentration of / h in lean CO2 gas, the rated power of the molten carbonate fuel cell is 80-120kW, preferably 100-110kW. Adopting the above-mentioned preferred embodiment facilitates stable output current of the molten carbonate fuel cell at the optimal operating voltage.

[0032] According to some preferred embodiments of the present invention, the volumetric flow rate ratio of H2 in the hydrogen-rich gas, CO2 in the CO2-lean gas, and O2 in the oxygen-containing gas is (0.8-1.2):1:(0.4-0.6), preferably (1-1.1):1:(0.5-0.55). Using the above preferred embodiments facilitates the transport of carbonate ions in an ideal 2:1 ratio of hydrogen and oxygen.

[0033] According to the present invention, the volume content of CO2 in the lean CO2 gas is not higher than 10%, preferably 10-20%. The method provided by the present invention can achieve the capture and utilization of low-concentration CO2, outputting electricity after electrochemical reaction in a molten carbonate fuel cell, and emitting high-concentration carbon dioxide, unreacted hydrogen, and water vapor in the anode tail gas, which is further obtained by catalytic combustion to obtain a CO2-rich mixture of water vapor and high-concentration CO2.

[0034] The present invention does not particularly limit the source of the lean CO2 gas. Preferably, the lean CO2 gas comes from the flue gas of a coal-fired power plant and / or the flue gas of a chemical plant.

[0035] More preferably, the method further includes: treating the flue gas from coal-fired power plants and / or chemical plants with dust before feeding it into the cathode of the molten carbonate fuel cell. Dust removal helps to avoid contamination and damage to the electrodes and membrane of the molten carbonate fuel cell.

[0036] According to the present invention, preferably, the oxygen-containing gas in step (1) is air.

[0037] In this invention, lean CO2 gas and oxygen-containing gas can be fed into the cathode of a molten carbonate fuel cell separately, or lean CO2 gas and oxygen-containing gas can be mixed and then fed into the cathode of a molten carbonate fuel cell.

[0038] To ensure sufficient reaction at the cathode side of the molten carbonate fuel cell, in a preferred embodiment, lean CO2 gas and oxygen-containing gas are first mixed and then fed into the cathode of the molten carbonate fuel cell.

[0039] In this invention, the hydrogen-rich gas may include hydrogen and optionally non-hydrogen gases. Preferably, the hydrogen volume concentration in the hydrogen-rich gas is not less than 80%, and more preferably 90-100%.

[0040] In this invention, the hydrogen-rich gas can be derived from fuel gases such as natural gas, coal-to-syngas, and hydrogen-containing purge gas from chemical plants. Preferably, the method includes: processing the fuel gas to obtain hydrogen-rich gas. Depending on the fuel gas source, the fuel processing method can include at least one of the following: natural gas reforming, coal-to-syngas water-steam shift reaction, and membrane purification, such as palladium membrane hydrogen purification. Any method that can convert the fuel gas into a hydrogen-rich gas that meets the above concentration requirements is acceptable. Those skilled in the art can select the appropriate method based on the specific fuel gas.

[0041] According to some preferred embodiments of the present invention, the method further includes: preheating the hydrogen-rich gas to above 100°C and then feeding it into the anode of a molten carbonate fuel cell. The preheating can be performed using any conventional method in the art, such as heat exchange in a heat exchanger. Preferably, the heat source of the heat exchanger can be low-quality waste heat from chemical plants, nuclear power plants, etc.

[0042] More preferably, the method further includes: recovering the heat from catalytic combustion to preheat the hydrogen-rich gas. Adopting the above preferred embodiments helps to further improve the overall system's heat utilization rate, increase thermal efficiency, and reduce costs.

[0043] In this invention, there are no particular limitations on the conditions for the catalytic combustion, as long as the hydrogen in the anode tail gas can be converted into water vapor through the catalytic combustion in step (2). Those skilled in the art can make selections according to actual needs.

[0044] According to the present invention, preferably, the volume content of CO2 in the CO2-rich mixture is not less than 60%, and more preferably 70-90%.

[0045] Preferably, the CO2-rich mixture contains water vapor, with a water vapor content of 10-20%.

[0046] In this invention, the solid oxide electrolyzer has the conventional definition in the art. The solid oxide electrolyzer generally includes a hydrogen electrode, an electrolyte, an oxygen electrode, and connectors forming the stack. Its power and number of cells can be calculated based on the gas source. This invention does not impose any particular limitation on the specific materials of the components in the molten salt fuel cell; any conventional choice in the art can be used.

[0047] According to some preferred embodiments of the present invention, the hydrogen electrode of the solid oxide electrolyzer is Ni-YSZ (yttrium-stabilized zirconium oxide), the oxygen electrode is LSM (lanthanum-strontium-manganese) or LSCF (lanthanum-strontium-cobalt-iron) or other perovskite oxides, the electrolyte layer is YSZ (yttrium-stabilized zirconium oxide), and the operating temperature is 600-800℃.

[0048] Preferably, relative to 100 Nm 3 The rated power of the solid oxide electrolysis cell for CO2 in CO2-rich gas per hour is 400-600kW, preferably 400-500kW.

[0049] In this invention, supplementary water vapor can be introduced into the hydrogen electrode side of the solid oxide electrolyzer as needed. The amount of supplementary water vapor is preferably such that the feed to the solid oxide electrolyzer satisfies the following volumetric flow rate ratio: water vapor, CO2, and oxygen in the oxygen-containing gas is (0.8-1.2):1:(0.5-0.7), preferably (1-1.1):1:(0.5-0.6). It is understood that the water vapor originates from a CO2-rich gas mixture and optional supplementary water vapor. Using the above-described preferred embodiment facilitates the complete electrolysis of CO2 into CO.

[0050] In this invention, the gas produced on the hydrogen electrode side of the solid oxide electrolyzer is returned to step (1) to provide at least a portion of the hydrogen-rich gas. In this invention, the produced gas requires no treatment and can be directly reused. It can be reused to obtain hydrogen-rich gas after fuel gas processing, or it can be directly used to supplement hydrogen-rich gas. Based on the gas volume, the supply of fuel gas can be reduced, achieving efficient energy utilization.

[0051] According to a particularly preferred embodiment of the present invention, a method for electrolyzing carbon dioxide and water using a coupled SOEC-molten carbonate fuel cell, the method comprising:

[0052] (1) The fuel gas is subjected to fuel treatment to obtain hydrogen-rich gas; wherein the fuel gas is selected from at least one of natural gas, coal-derived syngas, hydrogen-containing purge gas from chemical plants and hydrogen.

[0053] Hydrogen-rich gas is preheated to above 100°C and then fed into the anode of a molten carbonate fuel cell. CO2-lean gas and oxygen-containing gas are fed into the cathode of the molten carbonate fuel cell for direct electrochemical power generation. The volume content of CO2 in the CO2-lean gas is no more than 10%.

[0054] (2) Catalytically combust the anode tail gas of the molten carbonate fuel cell to obtain a CO2-rich mixture; wherein the volume content of CO2 in the CO2-rich mixture is not less than 60%, and the volume content of water vapor is 10-20%.

[0055] (3) The CO2-rich mixed gas is fed into the hydrogen electrode side of the solid oxide electrolytic cell, and the oxygen-containing gas is fed into the oxygen electrode side of the solid oxide electrolytic cell for co-electrolysis reaction.

[0056] (4) Return the generated gas from the hydrogen electrode side of the solid oxide electrolyzer to step (1) to provide at least a portion of the hydrogen-rich gas.

[0057] A second aspect of the present invention provides a system for electrolyzing carbon dioxide and water using a coupled SOEC-molten carbonate fuel cell, the system comprising an anode gas supply unit, a cathode gas supply unit, a molten carbonate fuel cell unit, a catalytic burner, and a solid oxide electrolysis unit.

[0058] The anode gas supply unit includes a fuel gas supply device and a fuel processor connected in sequence;

[0059] The cathode gas supply unit includes a flue gas supply device, an air supply device, and a mixer that is connected to the flue gas supply device and the oxygen-containing gas supply device respectively.

[0060] The molten carbonate fuel cell unit includes a molten carbonate fuel cell, and the solid oxide electrolysis unit includes a solid oxide electrolyzer.

[0061] The anode gas supply unit is connected to the anode inlet of the molten carbonate fuel cell and is used to provide hydrogen-rich gas; the cathode gas supply unit is connected to the cathode inlet of the molten carbonate fuel cell and is used to provide CO2-lean gas and oxygen-containing gas.

[0062] The anode exhaust outlet of the molten carbonate fuel cell is connected to the feed inlet of the catalytic burner, which is used to send the anode exhaust gas of the molten carbonate fuel cell into the catalytic burner for catalytic combustion to obtain a CO2-rich mixture.

[0063] The outlet of the catalytic burner is connected to the hydrogen electrode side inlet of the solid oxide electrolysis cell, and the oxygen electrode side inlet of the solid oxide electrolysis cell is connected to the oxygen-containing gas supply device, so that the CO2-rich mixed gas and the oxygen-containing gas are sent into the hydrogen electrode side of the solid oxide electrolysis cell for co-electrolysis reaction.

[0064] The gas outlet on the hydrogen electrode side of the solid oxide electrolyzer is connected to the anode gas supply unit to provide at least a portion of the hydrogen-rich gas to the gas produced on the hydrogen electrode side of the solid oxide electrolyzer.

[0065] According to the present invention, preferably, in the cathode gas supply unit, a dust removal device is further provided between the flue gas supply device and the mixer for dust removal treatment of the flue gas.

[0066] According to the present invention, preferably, a gas-liquid separator is also provided between the catalytic burner and the hydrogen electrode side inlet of the solid oxide electrolyzer.

[0067] According to the present invention, preferably, heat exchangers are also provided between the anode gas supply unit and the anode inlet of the molten carbonate fuel cell, between the cathode gas supply unit and the cathode inlet of the molten carbonate fuel cell, between the anode tail gas outlet of the molten carbonate fuel cell and the feed inlet of the catalytic burner, and between the gas production outlet on the hydrogen electrode side of the solid oxide electrolyzer and the anode gas supply unit, so as to realize heat recovery and gas source preheating, improve the heat utilization rate of the overall system, and help reduce costs.

[0068] The present invention will be described in detail below through embodiments.

[0069] In the following embodiments,

[0070] Composition of molten carbonate fuel cell: anode is nickel electrode, cathode is nickel oxide, electrolyte layer is molten Li2CO3-K2CO3 eutectic with a molar ratio of 62:38 immersed in lithium aluminate ceramic membrane, operating temperature is 650℃.

[0071] The solid oxide electrolyzer consists of a hydrogen electrode layer of Ni-YSZ (yttrium-stabilized zirconium oxide), an oxygen electrode layer of LSM (lanthanum-strontium-manganese) or LSCF (lanthanum-strontium-cobalt-iron), and an electrolyte layer of YSZ (yttrium-stabilized zirconium oxide). The operating temperature is 600-800℃.

[0072] Example 1

[0073] like Figure 1As shown, natural gas (composed of methane, ethane, propane, etc.) is reformed by a fuel processor into hydrogen-rich gas with a hydrogen content greater than 90 vol%, and the natural gas flow rate is 25 Nm³. 3 / h, the H2 flow rate after reforming is 100Nm 3 / h, CO2 flow rate is 25Nm 3 The flue gas, after heat exchange and preheating, is fed into the anode of the molten carbonate fuel cell stack at a rate of / h. The flue gas emitted from a coal-fired power plant, after dust removal treatment, enters the cathode of the molten carbonate fuel cell stack. The CO2 concentration in the flue gas is 20%, and the calculated CO2 content is 100 Nm³. 3 / h. A 100kW molten carbonate fuel cell stack is configured to absorb this portion of the carbon dioxide, while a cathode input of 250Nm³ is required. 3 / h of air (50Nm) 3 (O2 / h). After the electrochemical reaction in the molten carbonate fuel cell stack, the CO2 emission in the anode tail gas is 125 Nm. 3 / h, the hydrogen utilization rate in the anode reaction of the battery stack is 70%, and the anode tail gas still contains 30Nm 3 The hydrogen gas, at a flow rate of [amount missing] / h, undergoes catalytic combustion to convert all unreacted hydrogen into water vapor. The resulting high-concentration CO2 and water vapor are then directly introduced into the hydrogen electrode side of the SOEC fuel cell stack, while air is introduced into the oxygen electrode side. Based on the CO2 flow rate, calculations indicate a 500kW SOEC fuel cell stack is required, necessitating an additional 125Nm³ of CO2 supply to the hydrogen electrode side. 3 For a water vapor concentration of / h, 70Nm³ / h needs to be introduced onto the oxygen electrode side. 3 The air supplied at a rate of / h is ultimately subjected to a co-electrolysis reaction within the SOEC fuel cell stack, resulting in a mixture of CO and H2 at the hydrogen electrode side, with a flow rate of 250 Nm³. 3 / h, this portion of the mixed gas is returned to the anode front section of the molten carbonate fuel cell stack for recycling. This is due to the newly added 250Nm 3 A mixture of CO and H2 gas at a flow rate of / h can be used to reduce the natural gas flow rate to 5Nm³ / h. 3 This capacity of [number] / h can also meet the power generation needs of a 100kW molten carbonate fuel cell system, forming a closed-loop cycle system. After this cycle, natural gas consumption is reduced by up to 80%, which is very effective in saving fossil energy consumption and reducing emissions of pollutants such as CO2.

[0074] Example 2

[0075] like Figure 1 As shown, natural gas (composed of methane, ethane, propane, etc.) is reformed by a fuel processor into hydrogen-rich gas with a hydrogen content greater than 90% (volume fraction), and the natural gas flow rate is 50 Nm³. 3 / h, the H2 flow rate after reforming is 200 Nm 3 / h, CO2 flow rate is 50Nm 3 The flue gas, after heat exchange and preheating, is fed into the anode of the molten carbonate fuel cell stack at a rate of / h. The flue gas emitted from a coal-fired power plant, after dust removal treatment, enters the cathode of the molten carbonate fuel cell stack. The CO2 concentration in the flue gas is 10%, and the calculated CO2 content is 120 Nm³. 3 / h. A 200kW molten carbonate fuel cell stack is configured to absorb this portion of the carbon dioxide, while the anode side requires an input of 500Nm³ / h. 3 / h of air (100Nm) 3 (O2 / h). After the electrochemical reaction in the molten carbonate fuel cell stack, the CO2 emission in the anode tail gas is 170 Nm³. 3 / h, the hydrogen utilization rate in the anode reaction of the battery stack is 70%, and the anode tail gas still contains 60Nm 3 The hydrogen gas, at a flow rate of [amount missing] / h, undergoes catalytic combustion to convert all unreacted hydrogen into water vapor. The resulting high-concentration CO2 and water vapor are then directly introduced into the hydrogen electrode side of the SOEC fuel cell stack, while air is introduced into the oxygen electrode side. Based on the CO2 flow rate, for a 700kW SOEC fuel cell stack, an additional 150Nm³ of CO2 needs to be supplied to the hydrogen electrode side. 3 For a water vapor concentration of / h, 100Nm³ / h needs to be introduced to the oxygen electrode side. 3 The air supplied at a rate of / h is ultimately subjected to a co-electrolysis reaction within the SOEC stack, resulting in a mixture of CO and H2 at the hydrogen electrode side, with a flow rate of 350 Nm³. 3 / h, this portion of the mixed gas is returned to the anode front section of the molten carbonate fuel cell stack for recirculation. This is due to the newly added 350Nm 3 A mixture of CO and H2 gas at a flow rate of / h can be used to reduce the natural gas flow rate to 40 Nm³ / h. 3 This capacity, at [value] / h, can also meet the power generation needs of a 200kW molten carbonate fuel cell system, forming a closed-loop cycle. After this cycle, natural gas consumption is reduced by up to 80%.

[0076] Example 3

[0077] like Figure 1 As shown, natural gas (composed of methane, ethane, propane, etc.) is reformed by a fuel processor into a hydrogen-rich gas with a hydrogen content greater than 90% (volume fraction), and the natural gas flow rate is 25 Nm³. 3 / h, the H2 flow rate after reforming is 100Nm 3 / h, CO2 flow rate is 25Nm 3The flue gas, after heat exchange and preheating, is fed into the anode of the molten carbonate fuel cell stack at a rate of / h. The flue gas emitted from a coal-fired power plant, after dust removal treatment, enters the cathode of the molten carbonate fuel cell stack. The CO2 concentration in the flue gas is 10%, and the calculated CO2 content is 50 Nm³. 3 / h. A 50kW molten carbonate fuel cell stack is used to absorb this portion of the carbon dioxide, while the cathode side requires an input of 125Nm. 3 / h of air (25Nm) 3 / h of O2). After the electrochemical reaction in the molten carbonate fuel cell stack, the CO2 emission in the anode tail gas is 75 Nm. 3 / h, the hydrogen utilization rate in the anode reaction of the battery stack is 70%, and the anode tail gas still contains 30Nm 3 The hydrogen gas, at a flow rate of [amount missing] / h, undergoes catalytic combustion to convert all unreacted hydrogen into water vapor. The resulting high-concentration CO2 and water vapor are then directly introduced into the hydrogen electrode side of the SOEC fuel cell stack, while air is introduced into the oxygen electrode side. Based on the CO2 flow rate, a 200kW SOEC fuel cell stack is configured, requiring an additional 50Nm³ / h of CO2 to be supplied to the hydrogen electrode side. 3 For a water vapor concentration of / h, 20Nm³ / h is required to be introduced onto the oxygen electrode side. 3 The air supplied at a rate of / h is ultimately subjected to a co-electrolysis reaction within the SOEC stack, resulting in a mixture of CO and H2 at the hydrogen electrode side, with a flow rate of 100 Nm³. 3 / h, this portion of the mixed gas is returned to the front section of the anode of the molten carbonate fuel cell stack, where it can be used for further power generation. However, due to the mismatch between the gas volume and the molten carbonate fuel cell stack and the SOEC stack, the utilization rate of the fuel gas is low, and the overall efficiency is slightly worse.

[0078] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for electrolyzing carbon dioxide and water using a coupled SOEC-molten carbonate fuel cell, characterized in that, The method includes: (1) Hydrogen-rich gas is fed into the anode of the molten carbonate fuel cell, and CO2-deficient gas and oxygen-containing gas are fed into the cathode of the molten carbonate fuel cell for direct electrochemical power generation. Wherein, the volume content of CO2 in the lean CO2 gas is not higher than 20%; (2) Catalytically combust the anode tail gas of the molten carbonate fuel cell to obtain a CO2-rich mixture; (3) The CO2-rich mixed gas is fed into the hydrogen electrode side of the solid oxide electrolytic cell, and the oxygen-containing gas is fed into the oxygen electrode side of the solid oxide electrolytic cell for co-electrolysis reaction. (4) Return the generated gas from the hydrogen electrode side of the solid oxide electrolyzer to step (1) to provide at least a portion of the hydrogen-rich gas.

2. The method according to claim 1, wherein, The operating temperature of molten carbonate fuel cells is 620-650℃; Preferably, relative to 100 Nm 3 The rated power of the molten carbonate fuel cell is 80-120kW, preferably 100-110kW, for CO2 in lean CO2 gas per hour.

3. The method according to claim 1 or 2, wherein, The volumetric flow rate ratio of H2 in hydrogen-rich gas, CO2 in CO2-lean gas, and O2 in oxygen-containing gas is (0.8-1.2):1:(0.4-0.6), preferably (1-1.1):1:(0.5-0.55).

4. The method according to any one of claims 1-3, wherein, The volume content of CO2 in the lean CO2 gas is 10-20%; Preferably, the lean CO2 gas comes from flue gas from a coal-fired power plant and / or flue gas from a chemical plant; Preferably, the oxygen-containing gas in step (1) is air.

5. The method according to any one of claims 1-4, wherein, The hydrogen volume concentration in the hydrogen-rich gas is not less than 80%, preferably 90-100%; Preferably, the method includes: treating the fuel gas to obtain hydrogen-rich gas; wherein the fuel gas is selected from at least one of natural gas, coal-derived syngas, hydrogen-containing purge gas from chemical plants, and hydrogen. Preferably, the fuel processing method includes at least one of natural gas reforming, water-steam shift reaction of coal-to-syngas, and membrane purification.

6. The method according to any one of claims 1-5, wherein, The hydrogen in the anode tail gas is converted into water vapor by the catalytic combustion described in step (2). The method further includes: recovering the heat of catalytic combustion to preheat the hydrogen-rich gas. Preferably, the method further includes: performing gas-liquid separation on the products of catalytic combustion to obtain a CO2-rich mixed gas; Preferably, the volume content of CO2 in the CO2-rich mixture is not less than 60%, and more preferably 70-90%. Preferably, the CO2-rich mixture contains water vapor, and the volume content of the water vapor is 10-20%. Preferably, relative to 100 Nm 3 The rated power of the solid oxide electrolysis cell for CO2 in CO2-rich gas per hour is 400-600kW, preferably 400-500kW.

7. The method according to any one of claims 1-6, wherein, The method further includes: introducing supplementary water vapor to the hydrogen electrode side of the solid oxide electrolytic cell, wherein the amount of supplementary water vapor satisfies the following: the volume flow rate ratio of water vapor, CO2 and oxygen in the oxygen-containing gas is (0.8-1.2):1:(0.5-0.7), preferably (1-1.1):1:(0.5-0.6).

8. A system for electrolyzing carbon dioxide and water using a coupled SOEC-molten carbonate fuel cell, characterized in that, The system includes an anode gas supply unit, a cathode gas supply unit, a molten carbonate fuel cell unit, a catalytic burner, and a solid oxide electrolysis unit. The anode gas supply unit includes a fuel gas supply device and a fuel processor connected in sequence; The cathode gas supply unit includes a flue gas supply device, an air supply device, and a mixer that is connected to the flue gas supply device and the oxygen-containing gas supply device respectively. The molten carbonate fuel cell unit includes a molten carbonate fuel cell, and the solid oxide electrolysis unit includes a solid oxide electrolyzer. The anode gas supply unit is connected to the anode inlet of the molten carbonate fuel cell and is used to provide hydrogen-rich gas; the cathode gas supply unit is connected to the cathode inlet of the molten carbonate fuel cell and is used to provide CO2-lean gas and oxygen-containing gas. The anode exhaust outlet of the molten carbonate fuel cell is connected to the feed inlet of the catalytic burner, which is used to send the anode exhaust gas of the molten carbonate fuel cell into the catalytic burner for catalytic combustion to obtain a CO2-rich mixture. The outlet of the catalytic burner is connected to the hydrogen electrode side inlet of the solid oxide electrolysis cell, and the oxygen electrode side inlet of the solid oxide electrolysis cell is connected to the oxygen-containing gas supply device, so that the CO2-rich mixed gas and the oxygen-containing gas are sent into the hydrogen electrode side of the solid oxide electrolysis cell for co-electrolysis reaction. The gas outlet on the hydrogen electrode side of the solid oxide electrolyzer is connected to the anode gas supply unit to provide at least a portion of the hydrogen-rich gas to the gas produced on the hydrogen electrode side of the solid oxide electrolyzer.

9. The system according to claim 8, wherein, In the cathode gas supply unit, a dust removal device is also installed between the flue gas supply device and the mixer for dust removal treatment of the flue gas.

10. The system according to claim 8 or 9, wherein, Heat exchangers are also provided between the anode gas supply unit and the anode inlet of the molten carbonate fuel cell, between the cathode gas supply unit and the cathode inlet of the molten carbonate fuel cell, between the anode exhaust gas outlet of the molten carbonate fuel cell and the feed inlet of the catalytic burner, and between the gas production outlet on the hydrogen electrode side of the solid oxide electrolyzer and the anode gas supply unit.

Images